Plant parasitic nematodes such as those belonging to the genera Meloidogyne, Heterodera, Pratylenchus and Xiphinema cause billions of dollars of damage each year to agronomic crops, vegetables, fruits, flowering trees and shrubs. Almost all major plant species are susceptible to infection by these pests, which typically affect the roots of host plants but also can damage above-ground parts including the stem, leaves and flowers. There is consequently a great need for control of these parasites, which in the past has been accomplished by the administration of chemical nematocides (such as 1,3-dichloropropene; 2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate; ethyl 3-methyl-4-(methylthio)phenyl-(1-methylethyl) phosphoramidate; and methyl N',N'-dimethyl-N-[(methylcarbamoyl)oxy]-l-thiooxamidimidate). Such compounds can be highly effective; however, many have been found to pose an environmental hazard, and in some instances the amount and/or frequency of use of such compounds has been limited by regulatory authorities with the result that their nematocidal effectiveness is compromised.
As a result, efforts have been made to identify effective means of suppressing nematode damage which avoid or reduce the use of chemical pesticides. One approach has been to employ, in place of chemical pesticides, nematocides of biological origin with specific modes of action and relatively safer toxicological profiles. Examples of such alternative nematocides include ABG-9008 (a metabolite of the fungus Myrothecium verrucaria, disclosed and claimed in U.S. Pat. No. 5,051,255, issued Sep. 24, 1991), and a combination of avermectins (or related compounds such as milbemycins) with fatty acids (as disclosed and claimed in U.S. Pat. No. 5,346,698, issued Sep. 13, 1994). Another approach has been to combine spores of Pasteuria penetrans, a bacterial parasite of nematodes, with organophosphate nematicides (as disclosed in Australian Patent No. 60573/86, published Jan. 29, 1987). However, the preparation of P. penetrans spores on an industrial scale is hampered by the fact that the organism is an obligate parasite and therefore must be grown on nematodes in situ and isolated from nematode-infested root digests. There remains, therefore, a need for improved means of nematode control which, if involving the use of chemical pesticides, provide for a substantial reduction in the amount of chemical used.